The present invention relates generally to improvements to bar code scanners and bar code scanning. More particularly, the invention relates to advantageous techniques for interpreting a scanner signal to obtain information about the size, shape, position and motion of an object in the scan field of the scanner and using this information to improve the accuracy of decoding of a bar code on the object.
Bar code scanners are used in a wide variety of applications, such as retailing, inventory control, customer identification and many other applications. Many bar code scanners are adapted to scan a bar code located on an object, when the object is placed within the field of view of the scanner. Many such scanners produce complex scan patterns in order to maximize coverage of an object, so that a bar code located on an object will produce a readable reflection, even if the bar code is located on a relatively obscure area of an irregularly shaped object.
Frequently, especially in retail settings, it is highly desirable to scan objects in a rapid fashion, with objects being scanned one after another at a rate of more than one object every two seconds. At times during the scanning of a succession of objects, the scanning of some of the objects may be impaired for any of a number of reasons. For example, missed scans may occur due to a failure of an operator to bring the bar code into the field of view of the scanner. Double scans may result from the scanning of the same bar code by different scan lines. A scan of a bar code may fail because of low legibility resulting, for example, from low contrast of the bar code or damage to the bar code. Incorrect placement of a bar code on an object may result in an incorrect identification of the product being entered into the transaction.
Among its several aspects, the present invention recognizes that many such difficulties maybe overcome if imaging information about the objects brought into the field of view of a scanner can be obtained and is properly used in conjunction with the decoding of bar codes on the objects. The signal produced by scanning an object can, if properly interpreted, provide information not only about the bar code on the object but also about the object itself. Techniques for interpreting a scanner signal to obtain imaging information about an object are described on xe2x80x9cMethods and Apparatus for Obtaining Imaging Information in Bar Code Scanners, U.S. Pat. application Ser. No. 10/264,758, filed on even date herewith and having a common assignee to the present invention and incorporated herein by reference in its entirety.
According to one aspect, the present invention provides advantageous techniques for interpreting a scanner signal produced when one or more objects are brought into a field of view of a scanner to produce imaging information about the objects. This imaging information is then used to improve the accuracy of decoding bar codes located on or associated with the objects. A bar code scanner according to one aspect of the present invention may suitably comprise a scanning laser beam typically reflected from a rotating mirror to produce a scan pattern emerging from one or more scan windows to strike an object placed in or moving through the field of view of the scanner. The scan pattern typically comprises a number of scan lines, with each scan line being a trace of the scanning laser beam. Upon striking the object, a portion of the light reflected from the scan pattern is reflected back into the scanner where it is collected and used to produce a scan signal. The scan signal typically includes low frequency and DC components resulting from diffusively reflected light from the surface of the object. If the scan pattern strikes a bar code on the object, the scan signal will typically also include high frequency components resulting from the reflections from the bar code.
The signal is conditioned and split in order to provide a signal to a bar code module used to decode and interpret any bar codes within the field of view of the scanner, and to provide another, identical signal, to a time and space module used to extract timing information from the scan signal and to interpret the timing information in order to provide spatial information about the object in the field of view of the scanner. Details of the operation of a presently preferred time and space module are provided in the U.S. application Ser. No. 10/264,758 referred to above.
The bar code module may suitably provide timing information to the time and space module. The timing information indicates when a bar code is detected, and this timing information can be used by the time and space module to estimate imaging information about the object or objects in the field of view of the scanner when the bar code is detected. This information may include the size, shape, position and direction of travel of the object or objects. The time and space module transfers the imaging information to the bar code module, which then uses the imaging information to assist in decoding the bar code or bar codes. For example, the imaging information may indicate that there are two objects each of which has its own bar code label within the field of view of the scanner at a time at which two bar codes are detected. This information can be used to establish that a double scan of a single bar code has not occurred and to allow for proper decoding of both bar codes. Conversely, the imaging information may indicate that there are two objects within the field of view of the scanner at a time when only one bar code is detected, allowing a determination and notification of a missed scan.
Other uses of the imaging information may advantageously include determining if the approximate size of a an object is consistent with the product identified by the bar code associated with the object, or using distance information to determine the approximate width of the scan beam when it strikes the bar code, to aid in decoding the bar code.
A more complete understanding of the present invention, as well as further features and advantages of the invention, will be apparent from the following Detailed Description and the accompanying drawings.